1. Field of the Invention
The invention concerns cosmetic compositions and methods using such compositions for topical application to human skin. More particularly, the invention concerns an improved system for the delivery of .alpha.-hydroxy compounds that overcomes formulation difficulties and improves sensory properties.
2. The Related Art
A soft, supple and flexible skin has a marked cosmetic appeal and is an attribute of normal functioning epidermis. As human skin ages with advancing years, the epidermis can become folded or ridged or furrowed to form wrinkles which signal the loss of youthful appearance and herald the transition to old age. This transition can even occur prematurely with young people, especially those who expose themselves to excessive doses of sunlight. Also, the outer layer of the epidermis, that is the stratum corneum, can become dry and flaky following exposure to cold weather, or excessive contact with detergents or solvents which result in loss of skin moisture. Thereby, skin loses its soft, supple and flexible characteristics.
Emollients such as fats, phospholipids and sterols have in the past been used to soften wrinkled or dry skin, but it is apparent that these emollients are only partially effective as a remedy for skin in poor condition.
The use of .alpha.-hydroxyacids for enhancing the quality of human skin following topical application thereto has been widely reported.
U.S. Pat. No. 4,105,782 and U.S. Pat. No. 4,105,783, both to Yu and Van Scott, disclose the use of amines or ammonium salts of .alpha.-hydroxyacids in the treatment of ache, dandruff and dry skin. U.S. Pat. No. 4,234,599 (Yu & Van Scott) proposes the use of .alpha.-hydroxyacids and their esters or amine salts in the treatment of keratoses. U.S. Pat. No. 4,363,815 (Yu & Van Scott) suggests the use of .alpha.-hydroxyacids or .beta.-hydroxyacids or ketoacids and their derivatives, in a composition for treating skin conditions. Most recently, U.S. Pat. No. 5,091,171 (Yu & Van Scott) reports the use of .alpha.-hydroxyacids, .alpha.-ketoacids and related compounds as topically effective in the treatment of warts, nail infections, age spots, wrinkles and aging related skin changes.
U.S. Pat. No. 4,424,234 (Alderson et al.) identifies C.sub.6 -C.sub.10 .alpha.-hydroxy carboxylic acids as agents for improving human skin, particularly with emphasis upon the conditions of dryness and flakiness. U.S. Pat. No. 4,612,331 (Barratt et al.) reports that .alpha.-hydroxyoctanoic acid when combined with a neutralizing agent such as an alkanolamine enhances the extensibility of the stratum corneum without the development of skin irritation normally occurring in the absence of the neutralizing agent.
Based on the foregoing disclosures, it is evident that .alpha.-hydroxyacids and .alpha.-ketoacids have been well established in the art as therapeutically effective for cosmetic and dermatologic conditions and disorders. Unfortunately, formulation chemists have had a difficult time in providing stable creams or lotions containing these compounds in their active forms. Moreover, it is also difficult to deliver these compounds to the skin in their active form without causing skin irritation.
Accordingly, it is an object of the present invention to provide a cosmetic composition stably incorporating an active form of .alpha.-hydroxyacids, .alpha.-ketoacids or related compounds in a cream or lotion.
It is another object of the present invention to provide a cosmetic composition containing .alpha.-hydroxyacids, .alpha.-ketoacids or related compounds which when applied to skin in relatively high concentrations will cause less skin irritation than previously achievable.
A still further object of the present invention is to provide a method for treating dry skin, warts, nail infections, age spots, wrinkles and aging related skin changes with compositions that are effective but impart less skin irritation than compositions utilized hitherto.
These and other objects of the present invention that will become more readily apparent from consideration of the following summary, detailed description and examples which follow.